Not really sure who to vote for tbh, people are making some excellent points.
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When August used Meteor he effortlessly blitzed Gildarts and Cana, but then exited it immediately.
So you can't really say that Meteor August couldn't beat Gildarts. If I'm being really honest, I think an August that went all-out, or one that even just used named spells, would
decimate Gildarts.
To be clear, I'm not trying to discredit Gildarts here, all-out/using named spells August would decimate anyone bar Zeref/Irene/Acno. But this is exactly why I don't think it's fair to say Meteor August
couldn't beat Gildarts, since he has the feats showing Gildarts couldn't even react to him.
Also, you say that Jellal's speed is pointless, but it's the answer to your earlier point:
Jellal's speed is exactly what would help him avoid being cubed.